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Composting Toilets

Why composting toilets?

Composting toilets save water, protect the environment, and reconnect nutrient cycles. They offer a simple solution for both urban and rural situations, reducing the need for expensive sewer infrastructure or septic systems. Composting toilets help protect rivers, lakes, bays, and oceans while reducing the amount of wastewater entering sewers; our failing sewer infrastructure discharges billions of gallons of untreated sewage into American waterways each year.


Dry toilets vs. Composting toilets

There are two processes to turn human feces into valuable nutrients, composting and dehydration. In a composting toilet, toilet paper and sawdust are added to the feces and the material composts as microorganisms, bacteria and fungi process it into rich humus, killing any pathogens. Urine is either diverted or combined (combining it requires more sawdust to be used to soak up the excess liquid, and also causes odor issues). In a dry toilet, lime or ash is added to feces, urine is always diverted or evaporated, and toilet paper is not included. Feces dehydrate and pathogens die off. The end result is a crumbly, dry soil amendment, looking much like instant coffee. You can make either a dry or composting toilet, depending on your climate and the cover material available, either wood shavings or ash and lime.

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The majority of states do not have codes for composting toilets. All states have codes that require flush toilets connected to the sewer or septic systems, but currently no codes prohibit a composting toilet, as long as a flush toilet is also available. In general, composting toilets are not allowed as a replacement for a sewer hook up or a septic system, but are used on a "don't ask don't tell" basis. Washington, and Arizona are some of the states that do have composting toilet codes. Larger commercial scale projects do obtain permits for any use of composting toilets.

Composting toilets typically use no water, or very little water. Potential pathogens are killed by a variety of processes, including die-off and predation by other microorganisms as the material composts.

Follow these guidelines to help ensure safe and functioning composting toilets.

  • Isolation: The material should be left to compost in isolation, without potential contact from people, until it is fully composted and safe to handle.
  • Ventilation: The toilet needs a flow of fresh air to add oxygen and remove odors. All vents should exit the living space.
  • Moisture: A composting toilet should not be too wet. Urine diversion is recommended to help with excess moisture problems. If the toilet does not divert the urine, or if a small amount of water is added, the feces will need more dry material added or extra heating and mechanical mixing.
  • Temperature and time: The rate of decomposition is a function of temperature and time: the hotter the compost pile, the more quickly the decomposition process occurs. If the pile is not hot, the decomposition process slows down. If a humanure compost pile is not monitored for high temperatures it should be isolated for a long time to ensure full decomposition. In a mild climate this takes a year, while in areas with cold winters it may be 2 years.
  • Bulking agent: In a composting toilet sawdust covers the material creating air gaps for aerobic bacteria to break down the material. Toilet paper and feces compost through the same process a household food scrap compost bin undergoes. In a dry toilet ash or lime is mixed with soil and added to create a dehydrating environment for breakdown and die off of pathogens. Dry toilets are often used in arid, dry climates where lime and ash are more available than sawdust. Toilet paper can not be added to a dry toilet, it is usually burned or buried.


Composting Toilet Systems


Saw Dust Bucket Toilet

This is the simplest and lowest cost composting toilet. It was developed by Joseph Jenkin, composting toilet researcher and author of the classic book "The Humanure Handbook".

How it works: A 5 gallon bucket collects feces and urine, wood shavings are added after each use, and the bucket is emptied outside into a large composting receptacle where it composts. Most people make their own, Joseph Jenkins provides free plans on-line and also sells them (called the Loveable Loo).


Urine Diverting Sawdust Toilet

Urine is a high quality nitrogen fertilizer. If urine is separated from feces it can be used to fertilize the landscape, it also can make the composting process easier as excess liquid from urine can lead to odor and poor composting. You can make a urine diverting sawdust toilet which is similar to to the saw dust bucket toilet, with the addition of a urine diverting insert. Urine is collected separately from feces. The urine can be diluted with water (3-5 parts water per part urine) and used as a fertilizer, or it can be added to a backyard compost pile. The feces are composted separately.

Urine diverting toilets can also be purchased.



55 Gallon Drum Toilet:

If there is more room under the bathroom a larger compost receptacle can be used, such as a 55 gallon drum or a wheelie garbage bin.

Large-scale systems

Composting toilets can also be used in commercial scale applications. The company, Clivus Multrum, makes composting toilets for public restrooms, office buildings, as well as parks.